The goal of this effort is to develop a large-area, low-cost medical X-ray imager with image quality comparable with state-of-the-art digital medical imagers at a significantly lower X-ray exposure to the patient. The proposed imager will combine two technologies: porous dielectric materials and microwell electronic substrates. The porous dielectric material, such as 1 mm layer of CsI at 2% of nominal density, both converts incident X-rays to electrons and amplifies the electronic signal. This process creates around 100,000 electrons per photon rather than simply hundreds as for conventional detectors. Such a high gain results in a greatly increased signal to noise ratio, and hence better images at a lower dose. Microwell electronic substrates enable two-dimensional readout of the electrons generated in the porous dielectric. A microwell can be described as a two dimensional array of microscopic holes with an anode receptor at the bottom of each hole to detect the signal. Since both microwell substrates and porous dielectrics can be manufactured inexpensively and scale easily to large areas, the resulting detector will be large enough for medical imaging (up to 43cm x 43cm) and inexpensive. Resolutions greater than 10 lp/mm should be possible, enabling applications from general radiography to mammography. PROPOSED COMMERCIAL APPLICATIONS: The development of the proposed microwell porous dielectric detector would be revolutionary. Since it has better imaging capabilities than current technologies (superior sensitivity and signal-to-noise ratio at an equal resolution) and will be cheaper to produce, the microwell porous dielectric detector should find application to almost all areas of X-ray radiography from chest X-rays to mammography. It could also be used in scientific applications, such as X-ray diffraction and microscopy.